This invention relates generally to blades or buckets used in gas turbine engines and more particularly to applying dovetail seals to turbine buckets.
A gas turbine engine includes a compressor that provides pressurized air to a combustion section where the pressurized air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbine stages that extract energy therefrom to drive the compressor and provide useful work such as generating electricity or powering an aircraft in flight. Each turbine stage includes a plurality of circumferentially spaced apart blades or buckets extending radially outwardly from a rotor disk that rotates about the centerline axis of the engine. Each bucket is mounted on the rotor disk through the engagement of a dovetail portion in a corresponding disk slot. An airfoil portion extends radially outward into the hot combustion gas flow.
Because they are exposed to high temperature combustion gases, the buckets are ordinarily cooled to keep their temperatures within certain design limits. One common approach to cooling buckets is to pass a suitable coolant through an internal cooling circuit in the bucket. The coolant normally enters the internal cooling circuit through one or more inlets in the bottom of the bucket dovetail and exits through airfoil tip holes and/or cooling holes formed in the airfoil surface. Known cooling circuits often include a plurality of radially oriented passages that are series-connected to produce a serpentine path, thereby increasing cooling effectiveness by extending the length of the coolant flow path.
Since the dovetail inlets are in fluid communication with the disk slot in which each dovetail is located, the coolant is delivered to the inlets via the respective disk slots. However, leakage of coolant from the disk slots will result in reduced coolant flow to the bucket and a corresponding reduction in the service life of the bucket. Thus, it is desirable to seal leakage paths between each dovetail and the slot in which it is mounted. One approach to such sealing is to apply metal stripes to specified areas of the dovetail. When the bucket is mounted to the rotor disk by driving the dovetail into the slot, excess stripe material is sheared off, leaving a patch of material adhered to the dovetail and filling the corresponding gap between the dovetail and the slot. Accordingly, the corresponding portion of the slot is sealed.
Presently, the stripe material is ordinarily applied to the dovetail using thermal spraying techniques. This method requires extensive masking and is very time-consuming and expensive. Accordingly, it would be desirable to be able to apply dovetail seals quickly and inexpensively.